Fatty alcohols, i.e., predominantly linear, monohydric primary alcohols containing at least 8 carbon atoms, are important raw materials for the production of a number of products, for example, emulsifiers or surfactants. Fatty alcohols can be manufactured by catalytic high-pressure hydrogenation of fatty acid esters, preferably methyl esters. Typically, distilled methyl esters are passed in liquid form, together with a large excess of hydrogen, over fixedly arranged copper-containing mixed oxide catalysts, such as copper/zinc catalysts for example, at temperatures above 200.degree. C. and under pressures of around 250 to 300 bar. Fatty acid esters are used instead of fatty acids in order to protect the catalysts against attack by the free carboxyl groups. The process is described in detail in U.S. Pat. No. 5,180,858, the entire contents of which are incorporated herein by reference.
Carboxylic acid esters suitable for conversion to the corresponding alcohols via catalytic hydrogenation must contain little or no sulfur-containing compounds or metallic soaps such as sodium, potassium, and calcium in order not to poison the hydrogenation catalyst. Carboxylic acid esters, particularly fatty acid methyl esters used in the production of alcohols such as fatty alcohols prepared from the corresponding carboxylic acid and an alcohol using a sulfur-containing catalyst such as para-toluene sulfonic acid and subsequently treated with a base such as KOH to remove harmful and unwanted contaminants are particularly susceptible to sulfur- and soap contamination. In order to be able to use these esters for hydrogenation to the corresponding alcohols, the ester would have to at least be washed with water or, more typically, distilled to bring the amount of sulfur-containing compounds and soaps to acceptable levels.